The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to a method of fabricating an image sensor package.
Image sensors and assemblies are well known to those of skill in the art. In these assemblies, an image sensor was located within a housing which supported a window. Radiation passed through the window and struck the image sensor which responded to the radiation. For the image sensor to function properly, the image sensor had to be positionally aligned with the window to within tight positional tolerances.
Beaman et al., U.S. Pat. No. 5,821,532, hereinafter Beaman, which is herein incorporated by reference in its entirety, sets forth a printed circuit board which included a pair of apertures used as alignment features for mounting the image sensor and for mounting the optics which included the window. More particularly, the pair of apertures were used as the mounting reference for the image sensor and then were used as the mounting reference for the optics.
Formation of the assembly using the pair of apertures in the substrate as the alignment features resulted in at least three tolerance accumulations. First, a certain tolerance was associated with the formation, or patterning, of the metallic traces on the printed circuit board (see reference pads 14 and substrate 10 of Beaman FIG. 1). Second, a certain tolerance was associated with the placement of the image sensor on the substrate (see images sensor 32 and substrate 10 of Beaman FIG. 3). Third, a certain tolerance was associated the placement of the optics on the substrate (see Beaman FIG. 4).
After the image sensor assembly was constructed, the lens assembly was placed over the image sensor assembly. The lens assembly was used to focus light on the image sensor. Typically, the lens assembly was attached directly to the substrate after the image sensor assembly was attached to the substrate. After attachment, the lens assembly was adjusted, for example with adjustment screws, to move the lens assembly until the proper focus was attained. This very rough adjustment was labor intensive. Further, a large tolerance was associated with this very rough adjustment.
Disadvantageously, the image sensor assembly had to accommodate the tolerances discussed above. However, as the art moves to smaller, lighter and less expensive devices, the acceptable tolerances for image sensor assemblies diminishes.
In conventional image sensor assemblies, a housing was used to support the window and to hermetically seal the image sensor (see housing 24 and window 25 of Beaman FIG. 4 for example). This housing was typically formed of ceramic which advantageously had excellent resistance to moisture transmission to protect the image sensor from the ambient environment. Further, the ceramic housing was formed with a shelf which held the window and facilitated proper height positioning of the window (see shelf 29 and window 25 of Beaman FIG. 4 for example). However, ceramic is relatively expensive compared to other conventional packaging materials and it is important to form the image sensor assembly at a low cost.
In addition, mounting this housing at the printed circuit board level was inherently labor intensive and made repair or replacement of the image sensor difficult. In particular, removal of the housing exposed the image sensor to the ambient environment. Since the image sensor was sensitive to dust as well as other environmental factors, it was important to make repairs or replacement of the image sensor in a controlled environment such as a clean room. Otherwise, there was a risk of damaging or destroying the image sensor. Since neither of these alternatives are desirable and both are expensive, the art needs an image sensor assembly which is simple to manufacture and service so that costs associated with the image sensor assembly are minimized.
In accordance with the present invention, a plurality of image sensor packages are fabricated simultaneously to minimize the cost associated with each individual image sensor package. To fabricate the image sensor packages, a plurality of windows are placed in a mold. Molding compound is transferred to the mold to form a plurality of moldings, each of the moldings enclosing a corresponding window. The moldings are integrally connected together by bridge sections. After molding the windows in the molding compound, a molded window array, which includes the windows molded in corresponding moldings, is removed from the mold.
A substrate includes a plurality of individual substrates integrally connected together in an array format. Image sensors are attached to corresponding individual substrates. Bond pads of the image sensors are electrically connected to corresponding traces of the individual substrates.
The molded window array is aligned with the substrate such that each molding is precisely positioned with respect to the corresponding image sensor. After alignment, the molded window array is brought into abutting contact with an upper surface of the substrate such that an adhesive layer attaches the molded window array to the substrate. In one embodiment, the moldings are marked and a lower surface of the substrate is populated with interconnection balls. The substrate and attached molded window array are singulated into a plurality of individual image sensor packages.
By forming a plurality of image sensor packages simultaneously, several advantages are realized. One advantage is that it is less labor intensive to handle and process a plurality of image sensor packages simultaneously rather than to handle and process each image sensor package on an individual basis. Another advantage is that usage of materials is more efficient when a plurality of image sensor packages are fabricated simultaneously. By reducing labor and using less material, the cost associated with each image sensor package is minimized.
Of importance, the molding of the image sensor package is a low cost molded part. Advantageously, the molding is significantly less expensive than housings of the prior art which were typically ceramic. Accordingly, the image sensor package in accordance with the present invention is significantly less expensive to manufacture than image sensor assemblies of the prior art.
By forming the molding of the image sensor package as a molded part, a distance, sometimes called the Z height, between the window and the image sensor is precisely controlled to within tight tolerance.
Recall that in the prior art, the window was placed on a shelf of a housing after the housing was fabricated. Since a significant tolerance was associated with the window placement, the distance between the window and the image sensor had significant variations from assembly to assembly. However, to insure optimum operation of the image sensor, it is important that the distance between the window and the image sensor be precise. Since the tolerance in this distance is reduced in an image sensor package in accordance with the present invention, the performance of an image sensor package in accordance with the present invention is superior to that of the prior art.
In one embodiment, the molding of the image sensor package includes a plurality of alignment notches. These alignment notches are used to align a lens to the image sensor.
Use of the alignment notches facilitates alignment of the lens to the image sensor. As discussed above, the molding is precisely aligned to the image sensor. Advantageously, this allows the lens to be precisely aligned to the image sensor in a single operation by aligning the lens to the alignment notches. Accordingly, alignment of the lens to the image sensor in accordance with the present invention is relatively simple. This is in contrast to the prior art, which required a first alignment of the image sensor to the larger substrate and a second alignment of the optics to the larger substrate.
Enviro-hermetically sealing the image sensor in accordance with the present invention also reduces complexity and cost in the event the image sensor must be replaced compared to the prior art. As used herein, the term xe2x80x9cenviro-hermetically sealedxe2x80x9d means sealed sufficiently to prevent environmental degradation, e.g., from dust or moisture, of the image sensor package and, more particularly, of the image sensor.
Recall that in the prior art, the housing which hermetically sealed the image sensor was mounted directly to the larger substrate. Thus, removal of the housing necessarily exposed the image sensor to the ambient environment and to dust. For this reason, the image sensor had to be repaired or replaced in a cleanroom or else there was a risk of damaging or destroying the image sensor.
In contrast, the image sensor is enviro-hermetically sealed as part of the image sensor package in accordance with the present invention. The image sensor package is mounted to the larger substrate, for example, by reflowing interconnection balls. To replace the image sensor, the image sensor package is simply removed and a new image sensor package is mounted to the larger substrate. At no time is the image sensor exposed to the ambient environment during this procedure. Advantageously, this procedure can be performed in any facility with or without a cleanroom. The old image sensor package is discarded or shipped to a central facility for repair. Since the image sensor package is simple to manufacture and service, the costs associated with the image sensor package are minimized compared to the prior art.
In one embodiment, an image sensor package includes a molding having an interior locking feature and an exterior locking feature. The molding is integral, i.e., is one piece and not a plurality of separate pieces connected together. The image sensor package further includes a window having an interior surface and an exterior surface. The exterior locking feature of the molding contacts a periphery of the exterior surface of the window and the interior locking feature of the molding contacts a periphery of the interior surface of the window.
By having the molding extend over the peripheries of the exterior and interior surfaces of the window, the distance which moisture must travel along the interface between the molding and the window to reach the image sensor is maximized thus essentially eliminating moisture ingress into the image sensor package.
In another embodiment, an image sensor package includes a window and a molding, where the molding includes a lens holder extension portion extending upwards, e.g., in a first direction perpendicular to the exterior surface of the window, from the window. The lens holder extension portion includes a female threaded aperture extending upwards from the window such that the window is exposed through the aperture.
A lens is supported in a lens support. The lens support has a threaded exterior surface. The lens support is threaded into the aperture of the lens holder extension portion.
Advantageously, the lens is readily adjusted relative to the image sensor by rotating the lens support. More particularly, the lens support is rotated around a longitudinal axis of the lens support in a first direction, e.g., clockwise looking down at the lens support, to move the lens support and the lens towards the image sensor. Conversely, the lens support is rotated around the longitudinal axis in a second direction opposite the first direction, e.g., counterclockwise looking down at the lens support, to move the lens support and the lens away from the image sensor. In this manner, the lens support is rotated until radiation passing through the lens is properly focused on an active area of the image sensor. Once proper focus is attained, the lens support is prevented from unintentional rotation. For example, adhesive is applied to secure the lens support to the molding.
Recall that in the prior art, the lens assembly was typically attached directly to the larger substrate, such as a printed circuit mother board, after the image sensor assembly was attached to the larger substrate. A large tolerance was associated with attachment of the lens assembly in this manner. However, it is important to reduce tolerance buildup to optimize performance of the image sensor assembly.
Further, the lens assembly of the prior art typically had to be adjusted by moving the lens assembly relative to the larger substrate, for example with adjustment screws. Undesirably, this was labor intensive which increased the cost of the electronic device which used the image sensor assembly.
In addition, the lens assembly of the prior art was sometimes inadvertently moved relative to the image sensor which caused defocusing and defective operation of the image sensor. For example, the lens assembly was sometimes bumped during assembly or servicing of the electronic device which used the image sensor assembly. As another example, the lens assembly moved due to warpage of the larger substrate.
Advantageously, the image sensor package in accordance with the present invention eliminates these problems of the prior art. In particular, since the molding including the lens holder extension portion is precisely positioned with respect to the image sensor, the position of the lens with respect to the image sensor is also precise to within tight tolerance. Reducing tolerance in the position of the lens with respect to the image sensor improves performance of the image sensor package compared to prior art image sensor assemblies.
Further, the lens is adjusted relative to the image sensor simply by rotating the lens support thus readily allowing focusing of radiation on the active area of the image sensor. Advantageously, this focusing is performed during fabrication of the image sensor package before assembly to the larger substrate. Thus, the prior art requirement of focusing the lens assembly during assembly of the larger substrate is eliminated. As a result, the costs associated with the image sensor package is lower than that associated with prior art image sensor assemblies.
Further, since the lens support and the lens are integrated into the image sensor package, there is essentially no possibility of inadvertently moving the lens relative to the image sensor. Thus the prior art possibility of bumping the lens assembly or otherwise having the lens assembly move and defocus the radiation is eliminated.
In another embodiment, an image sensor package includes a molding having a locking feature. The package further includes a snap lid having a tab, where the tab is attached to the locking feature of the molding.
To form the image sensor package, after the molding is fabricated, a window is placed in a pocket of the molding. A shelf of the molding contacts and supports a peripheral region of an interior surface of the window. The snap lid is secured in place. Once secured, the snap lid presses against a peripheral region of an exterior surface of the window.
Of importance, the window is sandwiched between the molding and the snap lid. In this manner, the window is held in place. Advantageously, use of the snap lid allows the window to be kept in a protective wrapper until the window is needed. For example, the window is kept in a protective wrapper to avoid contamination or scratching of the window.
As a further advantage, use of the snap lid allows the window to be easily removed. Once removed, the window is easily cleaned, treated or replaced with a different window.
Also in accordance with the invention, a molded window array includes a plurality of moldings integrally connected together and a plurality of windows. Each window of the plurality of windows is support in a corresponding molding of the plurality of moldings.
These and other features and advantages of the present invention will be more readily apparent from the detailed description set forth below taken in conjunction with the accompanying drawings.